1. FIELD OF THE INVENTION
This invention relates generally to apparatus for converting television signals from one system to another and, more particularly, to apparatus for correcting the movement of a television image which is present in a field number conversion system.
2. DESCRIPTION OF THE BACKGROUND
Systems for converting from the NTSC system to the PAL system, or vice versa, are now known and an example of one such system is Japanese Patent Publication No. 48166/1972. Nevertheless, no consideration is made to correcting any movement errors of the image in such field conversion system. On the other hand, the technology for obtaining an interpolated image using the representative movement vector has been set forth in Japanese Patent Publication No. 28392/1985. Furthermore, a field conversion system for converting from a high definition television (HDTV) system having 1125 lines, 60 fields to the NTSC system having 525 lines, 60 fields has been disclosed, for example, in Japanese Patent Publication No. 104866/1984.
In the case of field number conversion systems, some consideration should be given to image movement, for instance, in the case of converting from sixty fields to fifty fields, movement commands are formed by respectively multiplying the derived movement vector by the coefficients of 1/5, 2/5, 3/5, 4/5, and 1. The movement vector is typically derived in the form of x samples, y lines, where x and y are integers, and the input image is shifted in response to these scaled movement commands, thereby forming more accurately positioned output images. Generally the movement commands in both the horizontal and vertical directions are rounded to the nearest whole number, for example, by counting fractions over one-half as one and discarding anything less than one-half. Thus, it is known to shift the input image by x samples, y lines in response to movement commands when performing field number conversion.
It has also been found that as the unit amount of movement correction is reduced, the accuracy of the movement correction can be increased. Nevertheless, the accuracy in the vertical direction of conventional movement correcting apparatus can not exceed one line.